12s rigger prop

[snaps]

Hi.I have a 40 inch rigger that runs a lehner 2240/12 on 12s.Has a swordfish 240hv esc and 5800 mha lipos.I only want this boat for speed runs and would like feed back on prop sizes.Any help would be much appriciated.Thank you

[NativePaul]

Any prop capable of getting a 40" rigger up onto the plane is likely to be well over the 80A maximum efficiency and the 124A maximum amps that Lehner recommend for the high amp version of that motor (is it safe to assume that it is a high amp?), when spinning on 12s at over 50k rpm.

By speed runs do you mean SAWs, as in 2 passes with a short beak for the water to recover in between them, or do you want to be running on the plane for a couple of minutes doing a dozen passes, and are just much more concerned with straight line speed than cornering?

Running such an extreme setup is a gamble, start with a small prop and work your way up checking for heat after every single pass, then prop down a couple of steps again and run your pair of passes checking for heat again before propping back up. If I had to guess where you will find the edge for 2 passes per run, it would be at 47mm, but if you run longer, have a bad setup, or just have bad luck you could probably blow it on a 40mm.

[snaps]

Any prop capable of getting a 40" rigger up onto the plane is likely to be well over the 80A maximum efficiency and the 124A maximum amps that Lehner recommend for the high amp version of that motor (is it safe to assume that it is a high amp?), when spinning on 12s at over 50k rpm.

By speed runs do you mean SAWs, as in 2 passes with a short beak for the water to recover in between them, or do you want to be running on the plane for a couple of minutes doing a dozen passes, and are just much more concerned with straight line speed than cornering?

Running such an extreme setup is a gamble, start with a small prop and work your way up checking for heat after every single pass, then prop down a couple of steps again and run your pair of passes checking for heat again before propping back up. If I had to guess where you will find the edge for 2 passes per run, it would be at 47mm, but if you run longer, have a bad setup, or just have bad luck you could probably blow it on a 40mm.

I would like to do SAW passes.I have run this boat many times now and today i ran a 2 way pass with a prather 240 (53mm) prop with ease at 132kph.All came back cold with lipos at 4.08 volts per cell.The lehner motor is not a high amp.Thanks

[Fluid]

82 mph is a very low speed for that setup; my 4S rigger runs almost as fast dragging around a big turn fin. That motor (different wind) has set SAW records, it will handle short burts of high amp draw. Things are cool because the prop is very inefficient, slips a lot, and over-spins the motor. That is no wonder considering the OP is trying to send around 10 horsepower through the tiny, inefficient Prather. That is a large boat and requires an appropriate prop thrust cone.

Properly loaded rpm will likely be in the 50,000 range. Paul's advice about going slow and checking temps is very good, but the prop size recommendation is far too small. Whatever prop is used will need to be hardened if it isn't stainless steel, unheated props will flower-out the blades eventually at that rpm. If you want to stay with stainless keep going up in Prather sizes - 245, 250, even 255. Eventually the prop will hook up and you will get appropriate speeds.....or the amp draw will become too great and burn something up.

One thing we do not know is the rigger design and setup. This could account for the low speeds too. Photos and a description of sponson and strut depth might help.


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